Iron bus bar having copper layer, and method for manufacturing same

ABSTRACT

The present invention related to an iron bus bar coated with copper and a method of manufacturing the same. The present invention provides an iron bus bar including an iron core and a copper layer applied on the iron core, and a method of manufacturing the same. According to the present invention, an iron bus bar having high strength and durability as well as excellent electrical conductivity can be manufactured at low cost.

CROSS REFERENCE TO RELATED APPLICATIONS AND CLAIM OF PRIORITY

This patent application is a National Phase application under 35 U.S.C.§371 of International Application No. PCT/KR2013/004668, filed 28 May2013, which claims priority to Korean Patent Application No.10-2012-0056935, filed 29 May 2012, entire contents of which areincorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a bus bar and a method of manufacturingthe same, and, more particularly, to an iron bus bar coated with acopper layer having a thickness of several tens of micrometers and amethod of manufacturing the same.

BACKGROUND ART

In the past, a cable had been frequently used as a medium fortransmitting electrical energy, but, recently, a bus bar, having anadvantage of transmitting a larger amount of electrical energy by thesame volume of conductor, has been widely used as an alternative to acable. Such a bus bar must have excellent electrical conductivity, highstrength and excellent durability.

A bus bar is used in large industrial distribution boards orswitchboards requiring the installation of a large-capacity electricalenergy transmitting system as well as in small household distributionboards or switchboards. Such a bus bar is generally composed of a copperbar, and thus its thickness is changed depending on current capacity.

Since copper, which is a main raw material of a bus bar, mostly dependson import, it is sensitive to foreign copper prices. The price of copperis greatly changed every year, and the change in import price of copperis also increased, thus increasing the cost of manufacturing a bus bar.

Recently, in order to solve such a problem by reducing cost, decreasingweight and improving performance, a composite bus bar, which is formedby coating aluminum with copper or by coating an iron alloy with copper,has entered the market.

Such a composite bus bar is currently manufactured by clad bonding,hydrostatic extrusion or indirect extrusion. In clad bonding, acomposite bus bar is manufactured by rolling two or more metal materialsat high temperature to bond them together. In both hydrostatic extrusionand indirect extrusion, a layered composite bus bar is manufactured byinserting a billet having a predetermined shape into an extrusioncontainer.

However, the clad bonding method is problematic in that the rolling ofmetal materials is generally performed at high temperatures, but metalmaterials, such as copper, iron and the like, are oxidized at a lowtemperature of 200° C. or lower, and the thermal expansion rates thereofare different from each other, so these metal materials are not suitablybonded, thereby producing defective products in large quantity. Further,this clad bonding method is problematic in that manufacturing processesand equipment are complicated, thus increasing a production cost.

Meanwhile, the hydrostatic extrusion and indirect extrusion methods arealso problematic in that the treatment of a pressure transmissionsolvent is not easy, an extruder is large-sized and high-priced, themaintenance cost of the extruder is high, and the operation methodthereof is complicated, so the efficiency of a work is reduced, therebycausing the unit cost of a bus bar to increase.

SUMMARY

The present inventors made efforts to solve the above-mentionedproblems. As a result, they developed a technology of coating an ironcore with a copper layer to a thickness of several tens of micrometers,thus completing the present invention.

Therefore, an object of the present invention is to provide an iron busbar, which is configured such that an iron core, containing cheap ironhaving high strength despite having lower electrical conductivity thancopper, is uniformly coated with a copper layer to a thickness ofseveral tens of micrometers, thus exhibiting excellent electricalconductivity, durability and strength; and to provide a method ofmanufacturing the same.

Another object of the present invention is to provide an iron bus bar,wherein an iron core is pretreated before the formation of a copperlayer, and/or a buffer layer is formed between the iron core and acopper layer, thus improving the adhesion between the iron core and thecopper layer formed on the surface of the iron core; and to provide amethod of manufacturing the same.

Still another object of the present invention is to provide an iron busbar, wherein the grain size of a copper layer formed on the surface of airon core can be controlled, so the specific surface area and electricalconductivity thereof can be improved, thereby improving thecharacteristics of a bus bar and controlling the shape and size thereof;and to provide a method of manufacturing the same.

Still another object of the present invention is to provide an iron busbar, wherein the corrosion of a copper layer can be prevented, and/oradditional resistance reduction and high quality texture can be realizedby further post treatment on the surface of the copper layer; and toprovide a method manufacturing the same.

Still another object of the present invention is to provide an iron busbar which is configured to be optimized in the form of both small andmedium-sized bus bars; and to provide a method manufacturing the same.

The objects of the present invention are not limited to theabove-mentioned objects, and other unmentioned objects thereof will beclearly understood by those skilled in the art from the followingdescriptions.

In order to accomplish the above objects, an aspect of the presentinvention provides am iron bus bar, including: an iron core composed ofan iron-containing material; and a copper layer formed on the surface ofthe iron core to a thickness of 10 to 30 μm.

Here, the iron-containing material may be any one selected from thegroup consisting of pure iron, carbon steel, stainless steel, a Fe—Alalloy and a Fe—Cu alloy.

The iron bus bar may further include a buffer layer formed between theiron core and the copper layer.

The buffer layer may include: a first buffer layer formed on the ironcore to have a thickness of 1 μm or less from the surface of the ironcore and including iron in an amount of 92.4 to 100 wt % at theinterface thereof making contact with the iron core; and a second bufferlayer formed between the first buffer layer and the copper layer to havea thickness of 1 μm or less and including copper in an amount of 95.9 to100 wt % at the interface thereof making contact with the copper layer.

The buffer layer may be configured such that the first buffer layers andthe second layers are alternately and repeatedly formed two or moretimes.

The iron bus bar may further include a corrosion-resistant layer formedon the surface of the copper layer to a thickness of 1 μm or less.

The corrosion-resistant layer may include at least one selected from thegroup consisting of Sn, Cr, Zr, Ag and Cu.

The corrosion-resistant layer may include 0 to 15.9 wt % of any oneselected from the group consisting of Sn, Cr, Zr and Ag and 84.2 to 100wt % of Cu at the interface thereof making contact with the copperlayer.

The iron bus bar may further include an uppermost layer having athickness of 1 μm or less and including at least one of Ag and Ti, whichis formed on the surface of the corrosion-resistant layer.

Another aspect of the present invention provides a method ofmanufacturing an iron bus bar, including the steps of: preparing an ironcore; and forming a copper layer having a thickness of 10 to 30 μm onthe iron core by coating.

In the method, the step of forming the copper layer may be performed bysputtering.

In the method, heat treatment may be further performed at 200 to 300° C.during the sputtering or after the sputtering.

The method may further include the step of cleaning the iron core withplasma before the step of forming the copper layer.

The method may further include the step of forming a buffer layer on theiron core by coating before the step of forming the copper layer.

In the method, the step of forming the buffer layer may be performed bythe sequential or simultaneous sputtering of buffer materials using twotargets. In this step, a voltage may be applied to an iron target andthen applied to a copper target at a predetermined time difference inorder to: form a first buffer layer on the iron core to have a thicknessof 1 μm or less from the surface of the iron core and to include iron inan amount of 92.4 to 100 wt % at the interface thereof making contactwith the iron core; and form a second buffer layer between the firstbuffer layer and the copper layer to have a thickness of 1 μm or lessfrom the surface of the first buffer layer and to include copper in anamount of 95.9 to 100 wt % at an interface thereof making contact withthe copper layer.

The method may further include the step of forming a corrosion-resistantlayer on the surface of the copper layer to a thickness of 1 μm or lessby coating.

The method may further include the step of forming an uppermost layerhaving a thickness of 1 μm or less and including at least one of Ag andTi on the corrosion-resistant layer by coating.

The present invention has the following advantages.

First, according to the present invention, an iron core, containingcheap iron having high strength despite having lower electricalconductivity than copper, is uniformly coated with a copper layer to athickness of several tens of micrometers, and thus an iron bus barhaving excellent electrical conductivity, durability and strength can bemanufactured in large amounts at low cost.

Further, according to the present invention, an iron core is pretreatedbefore the formation of a copper layer, and/or a buffer layer is formedbetween the iron core and a copper layer, thus improving the adhesionbetween the iron core and the copper layer formed on the surface of theiron core.

Further, according to the present invention, the grain size of a copperlayer formed on the surface of an iron core can be controlled, so thespecific surface area and electrical conductivity thereof can beimproved, thereby improving the characteristics of a bus bar andcontrolling the shape and size thereof

Further, according to the present invention, the corrosion of a copperlayer can be prevented, and/or additional resistance reduction and highquality texture can be realized by further post treatment on the surfaceof the copper layer.

Further, according to the present invention, the iron bus bar, which isconfigured to be optimized in the form of both small and medium-sizedbus bars.

DESCRIPTION OF DRAWINGS

FIGS. 1A to 1E are scanning electron microscope (SEM) photographsshowing the sectional images of iron bus bars obtained from Examples andComparative Examples.

FIG. 2 is a graph showing the results of thermal load testing of aspecimen according to an embodiment of the present invention.

FIG. 3 is a graph showing the results of thermal load testing ofspecimens according to other embodiments of the present invention.

FIG. 4 is a graph showing the temperature change transition of iron busbars obtained from Examples and Comparative Examples according to theresults of thermal load tests thereof.

FIG. 5 is a graph showing the temperature change of a coating layerapplied on an iron core with respect to the thickness change thereofduring a thermal load test.

FIG. 6 is a transmission electron microscope (TEM) photograph of asectional image of a multilayered buffer layer.

DETAILED DESCRIPTION

It will be further understood that terms, such as those defined incommonly used dictionaries, should be interpreted as having a meaningthat is consistent with their meaning in the context of the relevant artand the present disclosure, and will not be interpreted in an idealizedor overly formal sense unless expressly so defined herein.

Hereinafter, preferred embodiments of the present invention will bedescribed in detail with reference to the attached drawings.

Throughout the accompanying drawings, the same reference numerals areused to designate the same or similar components, and redundantdescriptions thereof are omitted.

The first technical characteristic of the present invention is toprovide an iron bus bar including a iron core composed of aniron-containing material and a copper layer formed on the iron core andhaving a thickness of several tens of micrometers, which is inexpensiveand has electrical conductivity equal to or higher than that of aconventional copper bus bar used in distribution boards or switch boardsmade of only copper. That is, the reason for this is that a conventionalcopper bus bar is problematic in that it is very expensive because it isentirely made of expensive copper, and in that its strength is low.

Therefore, the present invention provides an iron bus bar, including: aniron core composed of an iron-containing material; and a copper layerformed on the surface of the iron core to a thickness of 10 to 30 μm.

The structure of the iron bus bar of the present invention is attributedto a skin depth effect of most of electric current flowing through thesurface of a bus bar. That is, the iron core constituting the iron busbar of the present invention contributes to the improvement of thestrength thereof, and the copper layer formed on the surface of the ironcore to a thickness of several tens of micrometers to constitute theouter layer of the iron bus bar can be used as a channel of electriccurrent, thus allowing the iron bus bar of the present invention to havehigh strength and durability as well as excellent electricalconductivity. Like this, the iron bus bar of the present invention isadvantageous in that it can exhibit excellent electrical conductivitybecause of the copper layer formed on the surface of the iron core, andin that it is stable to thermal load because the iron core has highstrength and low density.

Firstly, the iron-containing material constituting the iron core of theiron bus bar of the present invention is very advantageous in terms ofcost reduction compared to copper or aluminum that has beenconventionally used. Meanwhile, based on the International AnnealedCopper Standard (IACS, %), the electrical conductivity of copper is103.06, that of aluminum is 64.95, and that of iron is 17.5. That is,the electrical conductance of copper is 5.8×10⁷ mhos/m, that of aluminumis 3.82×10⁷ mhos/m, that of iron is 1.03×10⁷ mhos/m, and that ofstainless steel is 1.1×10⁶ mhos/m. Therefore, iron is disadvantageous inthat its electrical conductivity is lower than that of copper. Incontrast, platinum used in coating an electrode of an electroniccomponent or used as an electrode material has an electrical conductanceof 9.52×10⁶ mhos/m, and solder used as a wiring material or bondingmaterial in the process of packaging an electronic component has anelectrical conductance of 7×10⁶ mhos/m. Considering these data, theelectrical conductance of iron is not at all inferior to that of othermetal materials.

The physical properties of copper, aluminum and iron are given in Table1 below.

TABLE 1 Class. Copper Aluminum Iron Density (g/cm³) 8.96 2.69 7.87Melting point (° C.) 1083.4 660.37 1535 Thermal expansion 16.5 23.6 11.7coefficient (10⁻⁶/° C.) Thermal conductivity 4.01 2.36 0.835 (W/cmK) at273 K Electrical conductivity 103.06 64.95 17.75 (% IACS) Electricalconductance 5.80 × 10⁷ 3.82 × 10⁷ 1.03 × 10⁷ (mhos/m) Specificresistance (μΩ · cm) 1.67 2.65 9.71 Yield strength (MPa)  69-365 215-415276-621 Tensile strength (MPa) 221-455 141-460 414-689

As given in Table 1 above, iron has excellent electrical conductivityand has high strength compared to copper, aluminum and other metalmaterials. That is, when the iron-containing material is used inmanufacturing a bus bar, the bus bar is imparted with high strength toexhibit excellent durability, and can thus be safely protected fromexternal shocks. Further, since the density of iron is about 88% that ofcopper, the weight of a distribution board or switchboard that uses alarge number of bus bars can be reduced by 10% compared to aconventional distribution board or switchboard, thus improving theworkability and transportability of the distribution board orswitchboard. Further, since the melting point of iron is about 1.4 timeshigher than that of copper, and is about 2.3 times higher than that ofaluminum, its thermal stability is also excellent.

When an air cooling load rapidly increases in summer, a large amount ofelectric current flows through a bus bar of a distribution board orswitchboard, and thus the temperature of the bus bar instantaneouslyincreases. In this case, the iron bus bar of the present invention isadvantageous in that it exhibits excellent durability and stabilityunder an environment influenced by stress together with thermal loadbecause it has relatively high durability and stability at hightemperature, and particularly, it has high yield strength and tensilestrength. Further, since the thermal expansion coefficient of iron isabout 70% that of copper, and is about 50% that of aluminum, the ironbus bar is advantageous in that its deformation ration is relatively lowwhen thermal load is generated due to the air cooling in hot summer.

As described above, it can be ascertained that the iron-containingmaterial constituting the iron core of the present invention is lighterthan copper in weight, is 1.5 times higher than copper and aluminum instrength, is superior to copper and aluminum in thermal stability anddurability, and is about 1/10 the price of copper.

Meanwhile, the iron-containing material constituting the iron core ofthe present invention is not particularly limited, as long as itcontains iron and has electrical conductivity. Preferably, theiron-containing material may include any one selected from the groupconsisting of pure iron, carbon steel, stainless steel, a Fe—Al alloyand a Fe—Cu alloy. In order to secure excellent electrical conductivity,the iron-containing material may include pure iron.

Next, the iron bus bar of the present invention includes a copper layerformed on the surface of the iron core. It is preferred that thethickness of the copper layer be 10 to 30 μm, which is optimal thicknessin the usable temperature range. When the thickness of the copper layeris less than 10 μm, the copper layer cannot secure the thicknesssufficient to obtain a skin depth effect, and thus the electricalconductivity of the copper layer may become lower than that of aconventional copper bus bar. Generally, the electrical conductivity ofthe copper layer is improved as the thickness thereof increases.However, when the thickness of the copper layer is more than 30 μm, thecost reduction effect thereof decreases, and the productivity thereof isreduced. That is, the electrical conductivity of the copper layer isimproved with the increase in the thickness thereof, but processing timeis excessively spent, the consumption of a raw material increases, andthe unit cost of processing increases, thus increasing the unit cost ofproduction.

The second technical characteristic of the present invention is that theiron bus bar of the present invention further includes: a buffer layerfor improving the adhesion between the iron core and the copper layer;and a protection layer for protecting the copper layer. That is,comparing the iron bus bar of the present invention with a conventionalcopper bus bar, in the case of the iron bus bar including the iron coreand the copper layer formed on the surface of the iron core, theadhesion between the iron core and the copper layer may become low, andthe electrical conductivity of the iron bus bar may be deteriorated whenthe copper layer having optimal thickness is damaged. However, when thebuffer layer is formed between the iron core and the copper layer, theadhesion between the iron core and the copper layer can be improved,stress can be controlled at a low level, and thermal load can bereduced.

Therefore, the iron bus bar of the present invention may further includea buffer layer between the iron core and the copper layer in order toimprove the physical properties thereof, such as the adhesion betweenthe iron core and the copper layer, and the like. The buffer layer mayhave thickness to such a degree that the copper layer is not separatedfrom the iron core. Preferably, the buffer layer may have a thickness of0.2 μm to 5 μm.

In this case, the buffer layer may be made of any one selected from thegroup consisting of Fe, Cu, Ni, Cr, Ti, Ta, Zr, Al, Mo, Ag and Au, but,in order to more improve the adhesion between the iron core and thecopper layer, the buffer layer may be made of two or more selectedtherefrom. That is, the buffer layer may be configured such that theinterface thereof making contact with the iron core contains a largeamount of iron, and the interface thereof making contact with the copperlayer contains a large amount of copper.

Particularly, the buffer layer may further include: a first buffer layerformed on the iron core to have a thickness of 1 μm or less from thesurface of the iron core and including iron in an amount of 92.4 to 100wt % at the interface thereof making contact with the iron core; and asecond buffer layer formed between the first buffer layer and the copperlayer to have a thickness of 1 μm or less and including copper in anamount of 95.9 to 100 wt % at an interface thereof making contact withthe copper layer. If necessary, the buffer layer may be configured suchthat the first buffer layers and the second layers are alternately andrepeatedly formed two or more times. Through the above configuration,the surface of the buffer layer can be made smooth, stress can bereduced, and the interlayer adhesion can be improved. In this case, thinfilms made of two or more kinds of materials and having predeterminedthickness may be alternately deposited in the form of several layers upto hundreds of layers.

Meanwhile, in order to protect the copper layer, that is, in order toimprove the corrosion resistance of the iron bus bar, the iron bus barmay further include a corrosion-resistant layer formed on the surface ofthe copper layer to a thickness of 1 μm or less. The corrosion-resistantlayer may include at least one selected from the group consisting of Sn,Cr, Zr, Ag and Cu. In order to increase the adhesion between thecorrosion-resistant layer and the copper layer, the corrosion-resistantlayer may include 0 to 15.9 wt % of any one selected from the groupconsisting of Sn, Cr, Zr and Ag and 84.2 to 100 wt % of Cu at theinterface thereof making contact with the copper layer. In this case, inorder to double the effect of improving adhesion, thecorrosion-resistant layer may include 100 wt % of Cu at the interfacethereof making contact with the copper layer, and the content of Cu maybe reduced as the distance from the surface of the corrosion-resistantlayer decreases.

Meanwhile, in the case where the entire corrosion-resistant layer isformed of an alloy of copper and other metal, in order for thecorrosion-resistant layer to protect the copper layer and to haveelectrical conductivity of 90% or more of that of the copper layer, thecorrosion-resistant layer may include 0 to 15.9 wt % of any one of Sn,Cr, Zr and Ag and 84.2 to 100 wt % of Cu. Among the metal elementsconstituting an alloy together with Cu, when Sn is included in an amountof 15.9 wt %, Cr is included in an amount of 1 wt %, Zr is included inan amount of 0.172 wt % and Ag is included in an amount of 8 wt % orless, the deterioration of electrical conductivity of the iron bus barcan be reduced, and simultaneously the corrosion resistance thereof canbe improved.

If necessary, the iron bus bar may further include an uppermost layerhaving a thickness of 1 μm or less and including at least one of Ag andTi, which is formed on the surface of the corrosion-resistant layer.That is, the uppermost layer serves to allow the iron bus bar to realizehigh-quality texture appearance by using silver color instead of coppercolor, and serves to improve the characteristics of the iron bus barbecause it includes silver, having low electrical resistance and havingelectrical conductivity equal to that of copper. Particularly, in thecase wherein the uppermost layer is made of an alloy of Ag and Ti, theiron bus bar can exhibit improved corrosion resistance as well asrealize high-quality texture appearance when the uppermost layer includeTi in an amount of 0 to 2 wt %.

The third technical characteristic of the present invention is toprovide a method of manufacturing an iron bus bar, by which a copperlayer having a thickness of several tens of micrometers can be formed onthe surface of an iron core by using sputtering, and grain size can becontrolled, thus manufacturing an iron bus bar having excellentcharacteristics in large amounts at low cost.

The method of manufacturing an iron bus bar according to the presentinvention includes the steps of: preparing an iron core; and forming acopper layer having a thickness of 10 to 30 μm on the iron core bycoating. If necessary, the method may further include the step offorming one or more of a buffer layer formed between the iron core andthe copper layer, a corrosion-resistant layer formed on the surface ofthe copper layer and an uppermost layer formed on the surface ofcorrosion-resistant layer.

First, in the step of preparing the iron core, the iron core may be madeof an iron-containing material in consideration of the desired size andshape of the iron bus bar.

Next, in the step of forming the copper layer by coating, in order toform a copper layer having a thickness of 10 to 30 μm, the copper layermay be formed by thickness-controllable sputtering. When the copperlayer is formed by sputtering, copper is uniformly applied on the ironcore, and the size of grains constituting the copper layer can becontrolled, thus improving the electrical characteristics thereof.

Meanwhile, due to the characteristics of an iron-containing material,treatment for removing an oxidation layer formed on the surface of theiron core may be performed prior to the preparation of the iron coreafter the formation of the copper layer. The reason for this is that theoxidation layer is formed on the surface of the iron core due to thecharacteristics of the iron-containing material, and thus the adhesionbetween the iron core and the copper layer decreases, thereby causingthe copper layer to be separated from the iron core. Consequently, whenthe copper layer is formed without removing the oxidation layer formedon the surface of the iron core, the iron core and the copper layer maybe separated from each other because of the oxidation layer existing onthe surface of the iron core. Therefore, in order to solve the problemwith the oxidation layer, a mechanical method using polishing orgrinding, a chemical method using an etchant or acid solution, a plasmatreatment method, or a method of inserting an oxide layer having highadhesion to the oxidation layer and having an effect of reducing stressmay be used. Further, it is preferred that the iron core besurface-treated and cleaned. The surface-treatment and cleaning of theiron core may be performed by all methods generally used in the relatedfields.

In an embodiment of the present invention, particularly, in order tosolve the problem with the oxidation layer, the iron core is cleanedwith plasma before the formation of the copper layer. That is, when theiron core is cleaned by plasma cleaning, that is, pre-sputtering, thereis an effect of etching the pollutants and oxidation layer remaining onthe surface of the iron core. The pre-sputtering, that is, plasmacleaning, including pretreatment may be performed for 30 to 60 min underthe conditions of a chamber pressure of 1 mTorr, a power of RF 1 kW andan Ar gas flow rate of 100 SCCM, and the pre-sputtering time may beadjusted depending on the amount of the iron core. During thepre-sputtering, ambient temperature may rise to about 80° C. In thiscase, the temperature in the vicinity of specimen also rises to about140° C. According to circumstances, grain growth is caused only by sucha temperature increase, thus the following additional heat treatment maynot be performed.

In the method of manufacturing an iron bus bar according to the presentinvention, when the step of forming a buffer layer on the iron core bycoating is further performed before the step of forming the copperlayer, this step is performed by sequential or simultaneous sputteringof buffer materials using two targets. In this step, a voltage isapplied to an iron target and then applied to a copper target at apredetermined time difference in order to: form a first buffer layer onthe iron core to have a thickness of 1 μm or less from the surface ofthe iron core and to include iron in an amount of 92.4 to 100 wt % atthe interface thereof making contact with the iron core; and form asecond buffer layer between the first buffer layer and the copper layerto have a thickness of 1 μm or less from the surface of the first bufferlayer and to include copper in an amount of 95.9 to 100 wt % at theinterface thereof making contact with the copper layer.

When a corrosion-resistant layer and an uppermost layer are furtherformed using two targets, similarly to the formation of the bufferlayer, the power can be sequentially or simultaneously applied to thetargets in consideration of adhesion at the interface contacting thecorrosion-resistant layer or the uppermost layer.

If necessary, one alloy target including the same metal as that includedin the buffer layer, corrosion-resistant layer and uppermost layer in apredetermined amount may be used instead of the two targets.

In the method of the present invention, the sputtering for forming thecopper layer, buffer layer, corrosion-resistant layer and uppermostlayer may be performed by coating the entire surface of the iron corewithout turning the iron core inside out using a rotation jig. Thissputtering may be performed for 30 to 300 min at a power of 4 to 5 kWdepending on the kind of targets and a base pressure of 5.4×10⁻⁶ Torr ormore.

Heat treatment may be simultaneously performed during the sputtering, ormay be performed at 200 to 300° C. after the sputtering.

For example, when the sputtering and the heat treatment are performedsimultaneously, the iron core may be heated during pre-sputtering,heated in situ during the formation of the copper layer, and heatedafter the formation of the copper layer. That is, when the iron core iscoated by pre-sputtering and sputtering, the iron core is previously putinto a vacuum chamber for sputtering, the vacuum chamber is made vacuum,the iron core is heated to about 200° C., and then heat treatment maystart. In this case, the degree of vacuum is maintained in high level of5×10⁻⁵ Torr or more. The process may be continued by applying heatduring the sputtering process. After the process, heat is additionallyapplied to 300° C. below for about 30 min to cause grain growth, thuslowering electrical conductivity. Such heat treatment is effective inlowering the temperature during the usage of a bus bar.

When heat treatment is performed after sputtering, for example, the heattreatment may be performed after the coated iron core is taken out fromthe vacuum chamber and then put into an atmosphere furnace or vacuumfurnace. In this case, the heat treatment may be performed at atemperature of 200 to 300° C. Even in the heat treatment, vacuum must bemaintained such that oxidation does not occur. It is preferred that thevacuum be a high vacuum of 5×10⁻⁵ Torr or more. It is considered thatheat treatment is performed under an argon atmosphere when it isdifficult to apply a vacuum atmosphere, but it is more preferred thatheat treatment be performed under a vacuum atmosphere.

Example 1

A copper target having a purity of 4N and a size of 450×120×6.35 mm andan iron core were provided, and then cleaned at a base pressure of5.4×10⁻⁶ Torr. In this case, the iron core was cleaned by plasmacleaning, and the plasma cleaning of the iron core was performed for 40min under the conditions of a chamber pressure of 1 mTorr, a power of RF1 kW and an Ar gas flow rate of 100 SCCM. Thereafter, sputtering wascarried out for 3 hr under the conditions of a chamber pressure of 1mTorr, a power of DC 5 kW and an Ar gas flow rate of 100 SCCM to coatthe iron core with copper, thereby obtaining an iron bus bar 1 (COB-13:number 13).

Example 2

An iron bus bar 2 (COB-14: number 14) was obtained in the same manner asin Example 1, except that the sputtering was performed for 5 hr.

Comparative Example 1

A comparative iron bus bar 1 (COB-10: number 10) was obtained in thesame manner as in Example 1, except that the sputtering was performedfor 1 hr.

Comparative Example 2

A copper target and molybdenum target, each having a purity of 4N and asize of 450×120×6.35 mm, and an iron core were provided, and thencleaned at a base pressure of 5.4×10⁻⁶ Torr in the same manner as inExample 1. Thereafter, first, molybdenum was sputtered on the iron corefor 29 min under the conditions of a chamber pressure of 1 mTorr, apower of DC 4 kW and an Ar gas flow rate of 100 SCCM, and then copperwas sputtered for 1 hour under the condition of a power of DC 5 kW tocoat the iron core with copper, thereby obtaining a comparative iron busbar 2 (COB-11: number 11).

Comparative Example 3

An iron core, a copper target and a molybdenum target were cleaned inthe same manner as in Comparative Example 2. Thereafter, copper andmolybdenum were simultaneously sputtered for 30 min under the conditionsof a chamber pressure of 1 mTorr, a power of DC 4 kW and an Ar gas flowrate of 100 SCCM to form a buffer layer. In this case, after themolybdenum target and the copper target were provided such thatmolybdenum and copper are simultaneously sputtered while opening ashutter, a substrate provided with an iron core was reciprocated infixed interval between the molybdenum target and the copper target toform molybdenum layers and copper layers corresponding to the number ofrevolutions, that is, to alternately form a plurality of thin firstbuffer layers made of molybdenum and a plurality of thin second bufferlayers made of copper, thereby forming a buffer layer having amultilayer structure (Mo/Cu/Mo . . . Mo/Cu/Mo). Thereafter, copper wassputtered on the buffer layer for 2 hr by a power of DC 5 kW to coat theiron core with copper, thereby obtaining a comparative iron bus bar 3(COB-12: number 12).

Experimental Example 1

The sectional images of the iron bus bars 1 and 2 of Examples 1 and 2and the comparative bus bars 1, 2 and 3 of Comparative Examples 1 to 3,which were observed by scanning electron microscope (SEM) to measure thetotal thickness of their respective coating layers, are shown in FIGS.1A to 1E, respectively.

From FIG. 1A, it can be seen that the iron bus bar 1 includes a coppercoating layer having a thickness of 11.6 μm. FIG. 1B shows that the ironbus bar 2 includes a copper coating layer having a thickness of 19.7 μm.Further, From FIGS. 1C to 1E, it can be seen that the comparative busbars 1, 2 and 3 include coating layers having thicknesses of 3.53 μm,3.86 μm and 8.27 μm, respectively.

Experimental Example 2

A commercially available aluminum specimen coated with copper, a generaluncoated iron specimen, a general uncoated copper specimen and the ironbus bar 1 of Example 1 were provided, and then thermal load teststhereof were carried out. In this case, these thermal load tests werecarried out using a thermal load tester. Each of the specimens having asection area of 2×15 SQ(30) was connected to the thermal load tester,and then electric current of about 100 A was applied thereto.Thereafter, the changes in temperatures of the specimens with respect totime were measured, and the results thereof are shown in FIG. 2.

From FIG. 2, it can be seen that the temperature of the copper specimen(copper) was 26.5° C., that of the aluminum specimen coated with copper(aluminum+copper) was 29.3° C., and that of the iron bus bar 1 ofExample 1 was 39.6° C. Considering the fact that a bus bar cannot beused when a thermal load is applied until the temperature of the bus barexceeds 40° C., the iron bus bar of the present invention can be used invarious fields. Meanwhile, it can be seen that the general uncoated ironspecimen (iron) cannot be used as a bus bar because its temperature isabout 48.4° C.

Experimental Example 3

The thermal load tests of a pure iron specimen, a pure copper specimen,the iron bus bar 1 (number 13) of Example 1 and the iron bus bar 2(number 14), each having a section area of 2×15 SQ (30), were carriedout under the condition of an electric current of 100 A or 80 A in thesame manner as in Experimental Example 2, and the results thereof areshown in FIG. 3.

From FIG. 3, it can be seen that the temperatures of the iron bus bars 1and 2 were all 35° C. or lower under the condition of an electriccurrent of 80 A, which is approximate to a real bus bar usage condition,and that their temperatures were approximately 40° C. even under thecondition of an electric current of 100 A, which is a severe condition.Particularly, it can be seen that the temperature of the iron bus bar 2was 31.1° C., which is the lowest temperature, under the condition of anelectric current of 80 A, and that its temperature was 36.7° C. evenunder the condition of an electric current of 100 A. Therefore, it canbe predicted that a coated iron core having performance similar to thatof a copper bus bar can be manufactured when a copper layer is appliedonto an iron core to predetermined thickness, that is, to a thickness of10 μm or more.

Experimental Example 4

The thermal load tests of the iron bus bar 1 (number 13), iron bus bar 2(number 14), comparative iron bus bar 1 (number 10), comparative ironbus bar 2 (number 11), comparative iron bus bar 3 (number 12) werecarried out under the same conditions as in Experimental Example 2, andthe temperature change trend curve of each of the specimens is shown inFIG. 4.

From FIG. 4, it can be seen that the comparative iron bus bar 2 and thecomparative iron bus bar 3, although each has a structure of ironcore/buffer layer/copper layer, have temperature unsuitable for actualuse, when the thickness of the copper layer applied on the iron core isless than 10 μm.

That is, comparing the comparative iron bus bar 1 (number 10) and thecomparative iron bus bar 2 (number 11), it can be seen that thethickness of the copper layer of the comparative iron bus bar 1 (number10) is 3.53 μm, and the total thickness of the comparative iron bus bar2 (number 11) is 3.86 μm, and thus the comparative iron bus bar 2(number 11) consists of a buffer layer (Mo) of 0.81 μm and a copperlayer of 3.15 μm. From the comparison, it can be ascertained that thethickness of the copper layer of the comparative iron bus bar 1 (number10) is greater than that of the copper layer of the comparative iron busbar 2 (number 11), but the total thickness of the comparative iron busbar 2 (number 11) is greater than that of the comparative iron bus bar 1(number 10) by 0.33 μm, so, as the results of thermal load tests, thetemperature of the comparative iron bus bar 2 (number 11) is lower thanthat of the comparative iron bus bar 1 (number 10) by about 4° C. Fromthe experimental results, it can be predicted that the buffer layer iseffective at decreasing the thermal load.

Further, comparing the comparative iron bus bar 2 (number 11) and thecomparative iron bus bar 3 (number 12), it can be seen that the totalthickness of the comparative iron bus bar 3 (number 12) is 8.27 μm, andthus the comparative iron bus bar 3 (number 12) consists of a bufferlayer (Mo/Cu multilayer structure) of 0.37 μm and a copper layer of 6.86μm. From the comparison, it can be ascertained that both the comparativeiron bus bar 2 (number 11) and the comparative iron bus bar 3 (number12) are provided with buffer layers, but actually, the thickness of thecopper layer of the comparative iron bus bar 3 is greater than that ofthe copper layer of the comparative iron bus bar 2 (number 11) by two ormore times, so, as the results of thermal load tests, due to the bufferlayer having a multilayer structure, the temperature of the comparativeiron bus bar 3 (number 12) is lower than that of the comparative ironbus bar 2 (number 11) by about 9° C., and is not greatly different fromthat of the iron bus bar 1 (number 13), as ascertained in the followingExperimental Examples.

Experimental Example 5

Thermal load tests for observing the temperature changes of specimensdepending on the thickness of a copper layer applied on an iron corewere carried out, and the results thereof are shown in FIG. 5.

As shown in FIG. 5, it can be ascertained that, as the results of thethermal load tests, the temperature of each of the specimens is lowerthan 40° C. only when the thickness of the copper layer applied on theiron core is 10 μm or more.

From the experimental results, it can be ascertained that the thicknessof the copper layer applied on the iron core must be 10 μm or more.

Experimental Example 6

The sectional image of the comparative iron bus bar 3 (number 12) ofComparative Example 3, which was observed by transmission electronmicroscope (TEM), are shown in FIG. 6.

From FIG. 6, it can be seen that the buffer layer formed on thecomparative iron bus bar 3 (number 12) has a multilayer structure inwhich a plurality of thin layers are deposited. Particularly, asdescribed above, the buffer layer formed on the comparative iron bus bar3 (number 12) was formed by alternately depositing thin films made oftwo different kinds of metals, that is, molybdenum and copper. FIG. 6shows that thin films respectively made of molybdenum and copper areclearly distinguished.

Meanwhile, it can be seen that the total thickness of the comparativeiron bus bar 3 (number 12) is 8.27 μm, and thus the comparative iron busbar 3 (number 12) consists of a buffer layer (Mo/Cu) of 1.37 μm and acopper layer of 6.86 μm, and that the comparative iron bus bar 1 (number13) consists of a copper layer of 11.60 μm. Comparing the thickness ofthe copper layer of the comparative iron bus bar 3 (number 12) and thethickness of the copper layer of the comparative iron bus bar 1 (number13), the thickness of the copper layer of the comparative iron bus bar 1(number 13) is greater than that of the copper layer of the comparativeiron bus bar 3 (number 12) by about 80%, and the total thickness of thecomparative iron bus bar 1 (number 13) is greater than that of thecomparative iron bus bar 3 (number 12) by about 40%.

However, it can be seen that the difference in thermal load testtemperature therebetween is 2° C. or less, which is very small. From theexperimental results, it can be predicted that the buffer layer having amultilayer structure of the comparative iron bus bar 3 (number 12) iseffective at decreasing the thermal load.

Although the preferred embodiments of the present invention have beendisclosed for illustrative purposes, those skilled in the art willappreciate that various modifications, additions and substitutions arepossible, without departing from the scope and spirit of the inventionas disclosed in the accompanying claims.

The invention claimed is:
 1. An iron bus bar, comprising: an iron corecomprised of an iron-containing material; a copper layer formed on thesurface of the iron core to a thickness of 10 to 30 μm; acorrosion-resistant layer formed on the surface of the copper layer to athickness of 1 μm or less; and a buffer layer formed between the ironcore and the copper layer, the buffer layer comprising: a first bufferlayer formed on the iron core to have a thickness of 1 μm or less fromthe surface of the iron core and including iron in an amount of 92.4 to100 wt % at an interface thereof making contact with the iron core; anda second buffer layer formed between the first buffer layer and thecopper layer to have a thickness of 1 μm or less and including copper inan amount of 95.9 to 100 wt % at an interface thereof making contactwith the copper layer; wherein the corrosion-resistant layer includes Cuand at least one selected from the group consisting of Sn, Cr, Zr andAg; the content of Cu in the corrosion-resistant layer reduced as thedistance from the surface of the corrosion-resistant layer decreases;and the buffer layer is configured such that the first buffer layer andthe second buffer layer are alternately and repeatedly formed two ormore times.
 2. The iron bus bar of claim 1, wherein the iron-containingmaterial is any one selected from the group consisting of pure iron,carbon steel, stainless steel, a Fe—Al alloy and a Fe—Cu alloy.
 3. Theiron bus bar of claim 1, wherein the corrosion-resistant layer includes0 to 15.9 wt % of any one selected from the group consisting of Sn, Cr,Zr and Ag and 84.2 to 100 wt % of Cu at an interface thereof makingcontact with the copper layer.
 4. The iron bus bar of claim 1, furthercomprising an uppermost layer having a thickness of 1 μm or less andincluding at least one of Ag and Ti, which is formed on the surface ofthe corrosion-resistant layer.